Designed Synthesis And Properties Of Novel Porous Metal-organic Frameworks

Recently, metal-organic frameworks?MOFs?, as a new class of organic-inorganic hybrid crystalline materials, have been attracted much interest from chemists and materialists. Compared with the traditional materials, MOFs not only have intriguing varieties of molecular architectures, but also possess many excellent and unique properties, including high surface area, tunable pore size, functional pore surface, etc.Hence, MOFs have widely potential applications in gas/liquid storage and separation,heterogeneous catalysis, magnetic, luminescence, sensor, drug delivery and so on.Many factors affect the structural assembly process of MOFs, such as organic ligand,metal ion/cluster, temperature, solvent system, synthetic method, template agent and so on. The current research work in this area is mainly focused on two aspects: the synthesis and properties of new MOFs; enhance the performance of the known MOFs via incorporation of functional groups. Herein, we focused on the synthesis of new MOFs and their widely applications. We successfully synthesized six different organic ligands were synthesized, including 1,3,5-tris?3,5-di?3,5-dicarboxyp henyl-1-yl?phenyl-1-yl?benzene(H₁₂TDDPB), 2,4-bis?3,5-dicarboxyphenylamino?-6-ol triazine?H₄BDPO?, pyridine-3,5-dicarboxylic?H₂PDC?,1,3,5-tri?4-carboxypheno xy?benzene?H₃TCPB?, 1,3,5-tri?4-?2H-tetrazol-5-yl?phenoxy?benzene?H₃TTPB? and1,3-di?4-carboxyphenyl?benzene?H₂DCPB?. These organic ligands can be applied as organic building blocks to assemble with transition metal to generate ten novel MOFs.Their structures and properties have been discussed in detail. The research work of this paper mainly includes the following four aspects:First, we designed and synthesized a rigid 12-carboxyl ligand, which were further assembled with Zn²⁺ and Cd²⁺ to form two different anionic MOFs, namely[Cd₁₅?TDDPB?4?H₂O?6]?18[H₂N?CH₃?₂]?18DMAc?1? and [Zn₃?TDDPB?]?2DMF?6[H₂N?CH₃?₂]?2?. There are two different Cd clusters, Cd₂?COO?₆ and Cd?COO?₄, in compound 1. In addition, there are two connection modes between TDDPB^12- ligands and Cd²⁺ ions to form three-dimensional?3D? porous structure. Due to open metal sites and dimethylammonium ions in compound 1, it exhibits high heat of adsorption of CO₂ and highly selective adsorption of CO₂ over CH₄. The rigid 12-carboxyl aromatic ligand has been successfully assembled with Zn²⁺ ion to obtain a 3D porous material, namely compound 2. The resulting MOF material can emit strong blue luminescence, which can be used as a sensor to detect the toxic and dangerous nitro aromatics by photo-induced electron-transfer.Second, we adopted two organic ligands containing both N-donors and O-donors,which were all assembled with Cu²⁺ to generate four novel 3D porous materials,namely [Cu₂₄?BDPO?₁₂?H₂O?₁₂]?30DMF?14H₂O?3?,?Cu₂I₂?[Cu₂PDC₂?H₂O?₂]₂?[Cu?MeCN?₄]I?DMF?4?,?Cu₄I₄?[Cu₂PDC₂?H₂O?₂]₂?4DMF?5? and?Cu₂I₂?[Cu₃PDC₃?H₂O?₂]?2MeCN?2DMF?6?. Due to the Cu₂?COO?₄ in these materials, they all have good stability and outstanding gas sorption properties. The organic ligand BDPO^4- contains the acidic?-OH? and alkaline?-NH- and-N=? functional groups, which can be served as buffer guards to prevent the assault from the acidic and alkaline media.Hence, compound 3 exhibits high stability in the acidic and alkaline solution. In addition, the resultant microporous MOF features both open metal sites(Cu²⁺) and Lewis basic sites, which render it with interesting performances in selective gas adsorption and catalysing the tandem one-pot deacatalization-Knoevenagel condensation reaction. On the other hand, three porous HKUST-like MOFs based on multi four-node copper clusters can be successfully synthesized via this reticularsynthesis approach. These porous materials all display commendable adsorption of CO₂ and high selectivity for CO₂ over CH₄ and N₂.Third, we synthesized two semi-rigid tripodal ligands with carboxylic acid or tetrazole groups, namely H3 TCPB and H3 TTPB. They can assembled with Zn²⁺, Cd²⁺and Cu²⁺ to generate three different two-dimensional?2D? porous layer structures,namely [Zn₃?TCPB?₂?H₂O?₂]?2H₂O?4DMF?7?, [Cu₃?TTPB?₂?H₂O?₆]?5DMF?8? and[Cd₃?TTPB?₂?H₂O?₆]?6DMF?9?. The resulting compound 7 can emit blue luminescence, which is preferable to the host framework with blue emission to tune different colors and generate white-light emission materials by introducing Eu³⁺?red?and Tb³⁺?green?. Compound 8 and compound 9 have similar structures. However, just compound 8 is stable in water, which is mainly attributed to the shorter bond length of Cu-N than that of Cd-N. From the results of liquid adsorptions, compound 8 exhibits selective sorption capability for H₂ O, MeOH and EtOH vapors, which has potential application of the separation of alcohol and water. On the other hand, compound 9displays an important luminescence property to detect toxic nitroaromatic explosives via luminescence quenching.Finally, we synthesized a V-shaped aromatic ligand H₂ DCPB, which can be assembled with Zn²⁺ to form a two-fold interpenetrated 3D porous framework with pcu topology, namely [?Zn₄O??DCPB?₃]?11DMF?5H₂O?10?. By luminescence technique, compound 10 can be served as the most efficient porous material-based sensors for TNP, the corresponding Stern-Volmer constant?KSV? is 3.7 × 104 M-1.Especially, compound 10 also can distinguish TNP?blue-shift? from the other nitroaromatic compounds?red-shift? through shift direction of luminescence spectra.